Digital controllers, such as process control units and PLCs (Programmable Logic Controllers), and the like are used for performing control processes in a discrete manner. Because of this, digital controllers repeat the operations of the programs by which to achieve the control operations at specific operating cycles. An example of this is disclosed in Japanese Unexamined Patent Application Publication 2002-351509, which is hereby incorporated by reference in its entirety. Increased levels of integration in microprocessors in recent years has led to increased speed in the processing capability of the microprocessors and compressed operating cycles. However, on the other hand, thought has also been given to the allocation, to each program, of the appropriate operating cycle, ranging from a short operating cycle to a long operating cycle, depending on the control process.
Conventionally, multiple programs having different operating cycles have been executed by multitasking operating systems (OS). However, simple time-sharing through a multitasking operating system cannot guarantee observance of the strict operating cycles of programs. Furthermore, it has been necessary to have complex procedures for assigning priority levels to each of the plurality of programs. In addition, thought has also been given to allocating the microprocessor processing capability in advance to those programs with short operating cycles and to those programs with long operating cycles. However, in some cases the number of programs actually operating does not correspond to the publications of processing capability that have been set in advance. Because of this, if, for example, there is a large number of programs with short operating cycles, the processing capability of the microprocessor, if allocated in advance to processing programs having short operating cycles, will end up being inadequate, while, on the other hand, if there are only a few programs with long operating cycles, then a situation will arise wherein there will be openings in the processing capability of the microprocessor, if allocated in advance to processing programs with long operating periods. The result is that there are problems in that the processing capability of the microprocessor is wasted.